1. Field of the Invention
The present invention relates to a store-and-forward switching system and, more particularly, to a store-and-forward switching system which is configured to define types of services which can be provided to each of terminal units.
2. Description of the Related Art
A conventional store-and-forward switching system is configured such that a plurality of facsimile terminal units are coupled to a facsimile store-and-forward switching unit (i.e. central unit) through a network. In such a system, all of services, such as Alternate recipient communication, Multi-destination delivery communication, information-box communication, P.O.-box communication, etc., that the central unit can provide are open to all the terminal units, and any terminal unit is free to request the central unit to provide all the services.
Thus, many terminal units may request the central unit to provide the same kind of service at the same time. In case where such simultaneous requests are made for Multi-destination delivery communication, a problem will arise in that it takes a long time to transmit information (e.g., information upon which a communication service request is made) requested by each terminal.
A concrete example of the case where such a problem arises is as follows. The Multi-destination delivery communication services are ranked according to priorities into SUPER HIGH-PRIORITY multi-destination delivery communication, HIGH-PRIORITY multi-destination delivery communication, NORMAL-PRIORITY multi-destination delivery communication, etc. For example, the system is constructed such that, when the central unit receives a service request for urgent multi-destination delivery communication from a terminal unit in the middle of the NORMAL-PRIORITY multi-destination delivery communication with another terminal unit, the central unit interrupts the NORMAL-PRIORITY multi-destination delivery communication and provides the SUPER HIGH-PRIORITY multi-destination delivery communication service. If, however, the right to accept the SUPER HIGH-PRIORITY multi-destination delivery service is provided to all the terminals, there will be the possibility that all the terminal units make a request for the SUPER HIGH-PRIORITY multi-destination delivery communication to the central unit. When such a situation occurs, the requests for the multi-destination delivery communication service of the same rank will increase and sometimes only the request for multi-destination communication of the same rank will be present. Thus, the ranking of the multi-destination delivery communication services becomes insignificant. As a result, a problem will arise in that the multi-destination delivery communication which is effective in case of urgency does not function properly.
As one of measures to solve such problems as described above, it will be considered to prohibit the central unit from performing the urgent multi-destination delivery communication service. However, when such a measure is taken, any terminal unit will not be able to send any urgent multi-destination delivery communications when necessary. Therefore, the multi-delivery communications function in case of urgent cannot be performed properly and any solutions of the problems cannot be brought about. Conversely, if a measure were taken at the terminal site to prohibit a predetermined type of service, then complicated control therefor would have to be performed. For example, a part, such as a magnetic card, would have to be added. This would increase the cost of each terminal. In addition concerning the system operation as well, there would be arisen a problem of such a complicated system operation that a desired service could not be provided without entering a password.
As described above, with the conventional store-and-forward switching system, since any terminal unit is given the right to cause the central unit to perform all the services, a situation can occur in which many requests for the same kind of service occur at the same time. As a result, a problem arises in that processes are delayed in the central unit, a requested service is not performed for a long time and the system performance is degraded. For example, in case where each of the terminal units makes a request for the SUPER HIGH-PRIORITY multi-destination delivery communication at the same time, its transmission will take a long time. That is, the SUPER HIGH-PRIORITY multi-destination delivery communication will be meaningless.